Controllable pitch propeller



July 19, 1949. J. STUART, In., ETAL 2,476,633

v CONTROLLABLE FITCH PROPELLER Filed Apr-11 s, 1944 2 sheets-sheet 1 INVENTOR f JDSEPH .n/HRT@ gz WHRRWEEEHM Ey #w3 MWL-M #7044 ATTOR N EY July 19, 1949.

Filed April 3, 1944 J. STUART, m., ETAL 2,476,638

GONTROLLABLE PITCH PROPELLER 2 Sheets-Sheet 2 ATTORNEY Patented July 19, 1949* UNITED STATES PATENT oi-Fica CONTROLLABLE FITCH PROPELLER Joseph Stuart, III, and Warren D. Berkley, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich., a 'corporation o! Delaware Application April s, 1944, serial Np. 529,261

1o claims. (ci. 11o-160.18)

This invention relates to propellers for aircraft, and particularly to those of the high-low pitch' position, or two position type of construction.

One object of the invention is tofprovide a propeller` for aircraft with alterable pitch blades, which can be manufactured at low cost and be serviceable for inexpensive craft.

Another object of the invention is to provide a. two-position propeller having a low'pitch position, such as is usually used for take-olf and climb operating conditions, and a high pitch position, such as is usually used 'for high speed night and cruising.

Another object of the invention is to provide a controllable pitch propeller characterized by a simplified operating principle and mechanism adapting it to inexpensive mass production.

Another object is to provide a propeller control mechanism obtaining a positive readily controlled operating force from the action of centrifugal force, and in particular, from the centrifugal fluid pressure of a dense fluid medium such as mercury rotating in a simple expansible chamber.

Another object of the invention is to provide a. controllable pitch propeller having no contacting relatively moving parts during cruising operation in the high pitch position.

Another object of the invention is to provide a controllable pitch propeller havingonly very lightly loaded moving parts in the low pitch Position.

A further object is to provide a controllable pitch propeller requiring only noncritlcal engagement` and/or disengagement of friction faces to eiect its control.

A further object is to provide a propeller pitch control utilizing friction controlling' means that have no relative motion except during the occasional brief intervals when the pitchis being changed which infers only zero and negligible power absorption in high and low pitch respectively.

A further object is to provide a controllable pitch propeller that is characterized by an axially symmetrical system that is by its very nature readily balanced.

A still further object of the invention is to provide a controllable pitch propeller capable of selective shift to either high or low pitch position while rotating, without requiring throttle adjustment of the engine, or other secondary manipulations. v

Another object of the invention is to provide invention will be apparent from the following 2 while the propeller is rotating to either a high pitch position, or to a low pitch position.

A further object of the invention is to provide an alterable pitch propeller that will effect pitch change in response to the action of a centrifugal fluid.

Another object of the invention is to provide an alterable pitch propeller with shiftable blades supported in the hub by a centripetall thrust bearing to assure ease of shift-in response to small or weak shifting forces.

Other objects comprehended by the invention include utilizing the centrifugal force or twisting moment of thebladesto return them to the low pitch position: providing a simple cockpit control giving a positive locked-in position, v

when necessary, and quick release, to avoid un'- necessary wear of the friction engaging surfaces; fluid seals for centrifugal iiuidpitch shifting units that suffer only. small occasional relative movements and are thus free of wear and other high rotational speed diinculties; low pitch blade increasing pitch force load transfer toa stationary nut; chrome plated or other corrosion resistant surfaces for theexpansion chamber; and a ball type preloading bearing located on the blade pitch changing axis.

Further objects and advantages of the present description, reference .being had to the accompanying drawings wherein a preferred embodiment of the present invention Ais clearly shown.

In the drawings: Fig, 1- is a view partly in longitudinal section and partly in elevation of a propeller incorporatl ing the instant invention.

` Fig. 2 is a view of the manual controller therefor with the connection indicated by a dashed an alterable pitch propeller that can be shifted pitch propellers for aircraft has chiefly followed the desire and needs of the commercial vplane and the war plane, becoming too complicated structurally, too costly and too massive for use on the small craft, and particularly on privately owned craft. Attempts have been made to fashion controllable pitch propellers suitable for the small craft owner, but following the trends of development for the larger craft they become impracticable for the lesser powered machines.4

their advantages are overshadowed by loss of split cone 22 to crowd the hub against a rear cone '24, whileV a lock device 28 insures that the nut and .shaft win not loosen. rne hub u sockets a plurality of propeller blades 28 by means of sockets 30 having stack bearings 32 to journal themaneuverability, flight Speed. ghl rangefandu' Y lstack 32. which in turn abuts against a blade reexcessive cost. Some of the .simplerv proposals incorporate relatively moving partstht are'rnore or less subject .to constant -wear while-the pr'opeller is operating, or at leastwhilepperatingfl; under a particular set of conditions-such.

Vnite length, iso, that the blade in rotating within during one of the pitch settings. Insome yinf-- stances, there is a slipping of friction faces throughout the operation in one or.l more pitchy settings. With many bf the devices of that character itfis necessary to alter the` engine speed before the contemplated blade pitchsettingcan "be made. VI'Ifhepresent invention vaccomplishes the end'v soughtby others, but-,overcomes their e handicaps by providing a propellerpitch control operating on a simple principle of centrifugal motion. ILinkage fromthe mass to the `blades is such that the stresses lon the. pitch change mechanism are at a minimum, and in some cases non-existent. The number of relatively `.movable parts are at a minimum, and wear between relatively movable parts is reduced to that brief .interval of time during which the blades are being moved from one pitch position to another position, in fact only during the start of such shift. With the disclosed embodiments it is not necessary to alter the engine speed when a change in blade pitch setting is made.

According to the invention an airscrew is provided in which a low pitch setting and a high pitch setting are always available at the option of the pilot. `The propeller blades are so characterized that they normally seek a low pitch position in response to centrifugal and aerodynamic forces applied to the blade during its rotation.

-The changes from low pitch to high pitch, and

viceversa, are effected bythe response of a rotating fluid medium or other mass to centrifugal force applied under the controlv of the pilot,

which he may apply at any time. To shift to the container for the fluid, and the built-in characteristics of the blades make them seek the low pitch position. When it is desired to change the pitch of the propeller all that is necessary is for the pilot tonmanipulate-the control member in the cockpit. Moving it to one position effects a shift to the high pitch' position and moving it Y to .another position effects a shift to the low pitch position.

lReferring particularly to the drawings, I il indi- .,cates an engine nose or gear casing from which, ,extends a rotatable engine driven propeller shaft the end lof; the blade* rootsu'pportsf' the thrust plate 38 While a blade nut 42 secured to the blade root transmits centrifugal forces to the bearing "taining uxut 48 by which the bearing mount of the blade may be preloaded. The blade cap 40 also provides alug 48 extending generally toward the axis of propeller rotation into a slot 48 of denits socket is limitedby the extent of movement of Vthe lug I6 along the length of the slot 48. The blades 2B are so proportioned and characterized that, while yrotatingtheywould normally seek the low pitch position, such thatthelug 46 would be at the right hand endV ofthe slot 14,8 substantially as shown in'Fig. 1 of the drawings in the case of a right hand propeller.- o

.In :that vposition a ,the 'blades' wellne- -46 has .i pushed .aft a. pin 58vcarriedfin abore 52 of the hub, that is arranged ,substantially parallelwith v the axis of rotation, and which pin` extends out .thelaft `face of the hub where itpasses through a seal ...and retainers 53 and`54respectively- A The pins 5U are slidable along` the Vbore .752 andareA of such lengththat they are', always engageable with a flange 56 of an axially movable shifting sleeve 58 coupled tothe active elementof a pitch shifting unit 60 carried by the hub.

The pitch shifting unit is shown in partially separated and broken perspective in Fig. 4 and in assembled-relation in Figs. 1 and 3, where the parts occupy the low pitch and high pitch positions respectivelyl The unit per se comprises a stepped cylinder 62 having a relatively small cylindrical surface 84 joined by an annular plane surface 66 to a relatively large cylindrical surface 68, and is tted with a stepped piston 'l0 having a relatively small cylinder 'I2 fitting the 'surface 64 and a relatively large cylinder M fitting the surface 68, the two pistons being `ioined by a plane surface 18 mating with and disposed opposite to the plane surface 66. The plane surface ,16 is annular and is carried radially inward to join the walls 18, 80 and 82 forming an annular groove V84 provided by the piston member. The groove 84 forms an annular reservoir between the piston and cylinder, which provides a definite minimum volume to be charged with a quantity. of fluid medium 86 of relatively high density. Mercury is the preferred material for such charge, but it is comprehended that other mediums are `suitable for the same uses. In any instance the portions of the piston and cylinder coming in contact with the mercury or other selected fluid should be treated to prevent corrosion, amalgamation or lother `deteriorating effects, and the jointsbetween assembled parts subjected to the medium should betreated or fashioned to avoid leakage or other loss of the medium. In the present instance appropriate seal rings 88 and 90 are set in the piston portions 12 and 14 respectively. I

l2 drivinglyengaging a. propeller hub I4 through the splines I6 and I8. where the parts Vare maintained by .a shaft nut 28 operating through a ananas hub or stand at rest relative to the engine nosing while the hub rotates within it. The bearing 94 is disposed with its races between the shifting sleeve 58 and the small cylinder 62 while the bear, ing 96 is disposed between a concentric flange 98 of the piston and a nut threaded on the hub extension 92 the nut securing the assembly in place. The nut |00 also engages and clampsan annular plate |02 against turning relative to the hub and engages a thrust ring |04 by which the bearing 96 is retained against axial movement along the hul.` extension. The bearing 94 is fixed against movement axially of the shifting sleeve 58 and cylinder 62, but since the sleeve 58 is capable of movement axially of the shaft or hub extension 92, then the cylinder 62 and bearing 94 as a unit is capable of movement axially of the hub.

Axial movement of the cylinder is opposed only by the natural tendencies of the blades to seek the low pitch position, and the shift in either directionfis accomplished by controlling the rotation of the mass of fluid in thechamber 84.- Selective control or shiftingvofwunit `rotation is effected by a plurality offriction faces, one of which is a clutch f ace |08 carried by the annular plate |02 and consequently always rotatable with the hub I4. A friction face |08 of annular form is carried by a plate l I0 loosely assembled with the stepped piston 10 and continually urged by suitable spring means ||2 toward engagement wi-th the clutch face |06. The plate ||0 is arranged concentric with the flange 98 and bridges an i annular channel ||4 between the flange 98 and the outer diameter cylinder 14, the channel ||4 operating to house the spring means ||2. The plate ||0 also provides a plurality of outwardly extending lugs or tongues ||6 movably engaging in notches ||8 and |20 in the 'rim of the cylinder 62 and the piston 14 respectively to permit relative axial but not relative rotational motion therebetween. A brake face |22 provided byY an `axially displaceable ring |24 is capable of manipulation to engage and disengage the friction face |08, and in so doing controls the rotation of the shifting unit.

The ring |24 is supported by a fixed ring |26 through-the agency of fixed pins |28 in the ring |24 that project into cam slots |30 of the ring |26. A flange portion |32 is apertured at |34 to receive one end of a control wire or rod |36 extending from the pilots compartment. The supporting ring |26 is rigidly fixed to a flanged plate |38 that is held rigid from the engine nose I0, and concentrically disposed about the shaft |2 and about a piloting ring |40, by screw devices |42. Rigid and adjustable coupling ofthe ring |26 and the flanged plate |38 is accomplished by a plurality of screw devices |44 passing through notches or slots |46 of the ring |26 and threading 'into the ange of the plate |38, which when tightened hold the parts in such relation that the brake face may be engaged with and disengaged from the friction face by suitableoscillation of the ring |24. p Y

To effect oscillation of the ring |24, the rod or wire |36 is carried to a manual |50 located in the cockpit where it is accessible at all times =to the pilot. One form of such manual is shown in Fig. 2, where its operative connection to the shifting unit is shown by the dashed line represented at |36. A tubular housing |52 hasga ange |54 by which it is secured toa head `member |56 extruded at |58 to form a guide sleeve extending through a dash member or bulkhead `160 to be ntted with a retaining n ut lez. sudie through the sleeve |58 is a. knobbed rod |64 that is guided at the other end of the hbusing by. a stepped sleeve |56 beyond which the rod is connected with the wire |36. The' wall of the housing |52 is provided with a long slot |68 ending in an angular offset |69 and is adapted to guide the movement of a pin |10 set in the rod |64, while a spring |12 disposed within the housing and compressible between a7 part of the rod |64 and Ithe sleeve |66 normally urges the retraction of the rod from the oiset end of the slot |68. Considering the illustrated embodiment, it will be observed that manual depression of the rod |64 causes the spring |12 to be compressed as the pin |10 slides to the left along the slot |68. The spring |68 is so constituted and stressed in its assembly that when the pin L10 reaches the offset portion |69, that rotation of the rod is effected to dispose the pi'n treme position, since then the spring |12 is releasedf and projects the rod to the extended position shown in dotted lines. In the illustrated embodiment the extended position of the rod pulls upon the wire or cable |36 to oscillate the ring |24 so that the brake face |22 is disengaged from contact with the friction face |08 allowing the friction face to engage the clutch face |06. On the other hand depression of the vrod |64 engages the brake face with the friction face |08 and withdraws the friction face from the clutch face |06 substantially as shown in Fig.'1.

Thus, manipulation of the manual |50 provides forY either arrestment or rotation of the pitch shifting unit. When the shifting unit is arrested, that is, when it is restrained from rotating with the hub, the centrifugal responsive fluid 86 within the annular chamber 84 remains quiet and finds its own level in the chamber, substantially as il-` p lustrated in Fig. l. The blades 28 being free from any biasing influence except the centrifugal force and aerodynamic forces due to hub rotation, seek the low pitch position. When the shifting unit is permitted to rotate with the hub, the chamber 84 and its fluid content 86 is also rotated and the fluid is thrown against the cylindrical wall 64 from where it presses between the parallel faces 66 and 16 of the cylinder and piston. This last pressure causes the cylinder to move axially of the shaft relative to the piston. As it does so the cylinder carries with it the bearing 94'and the shifting sleeve 58 causing the ange 56 to press the pins 50 forward of the shaft to rotate theblades to the high pitch position as defined by the lug 46 abutting thev end of the slot 48 as shown irrFig. 3. Pressure relief for the relative movement of the piston and cylinder is afforded by an opening through the cylinder 62, and access to the chamber 84 for' charging it with the desired amount of centrifugal uid is afforded by a screw plug |82.

An alternative form' of the shifting "unit is 7 vides lugs or a flange 2|4 apertured at 2|6 to guide the ends of pins 2I8 supporting a friction face 220, while springs 222 surrounding the pins 2I8 and disposed between the ange 2M and friction face member 220 urge the friction face 220 toward engagement with the clutch'face |06 which has heretofore been described as carriedl by and driven by the hub extension 92. Similarly, a brake face 224 is operable by a lever 226 pivoted at 228 and actuated by the cable |36 to selectively engage the friction face 220 for arresting rotation of the shifting unit. From a glance at Fig. 5 it should be apparent that when the friction face engages the clutch face, then the shifting unit rotates with the hub and the centrifugal force of rotation causes the weights 206 to move out radially and in doing so push the pin 50 to the left for moving the blades 218 tothe high pitch position. Likewise, engaging the brake face 224 with the friction face 220 first disengages the friction face from the clutch face and then arrests rotation of the shifting unit, with a consequent inward movement of the weights 206. The blades are now free to respond to their natural tendencies in seeking the low pitch position.

In the illustrated embodiment of Fig. 1, the propeller is mounted on a hollow shaft I2, and the end of the shaft is closed off by a spinner |84 which engages within the shaft bore |86 of the hub I4. The spinner is held in place by a long screw device |88 threading into a yoke |90 whose arms are apertured to receive a tubular cross pin or bar |92 lodged in the wrench receiving apertures of the hub retaining nut 20. However, the

provisions of cannon re through the shaft may be retained by removal of the spinner, or by tting with a spinner having an axial opening registering' with the bore of the shaft I2. On the other hand, either type of spinner may be fashioned so as to enclose the hub and the root portion of the blades, as well as the shaft end only.

From the illustrated and described embodiment of the invention it should be apparent that applicants have provided a two position propeller pitch control that can be built inexpensively and serve the purpose of having a low pitch setting for take olf and climb, with an instant and positive control of shift to high pitch position for cruising, or other maneuvers. The shift to high pitch or to low pitch can be made at any instant that the pilot desires, and there is no need or requirement' for manipulation of the engine throttle when any shift in blade pitch is made. The principle of operation is simple, and the mechanism eiecting the shift is not subject to inadvertent disorganization or injury. The relatively moving parts are few and are so moved only at the time of shift from one `to another. Adaption of centrifugal force renders the shift always positive and readily controlled; coupling of the force tothe shifting means effecting a change to the high pitch posi'- tion, while uncoupling the force insures a shift pitch setting I to the low pitch position. When thepitch setting is in thev high pitch position there are no contacting relatively moving parts, and when in the' low pitch position there are but lightly'lo'aded relatively moving parts, such as the journal bearings 94, 96 and/or |94,| 96, where the load is confined to the thrust of the bladesyin the low pitch position, uponl Athe ends 'of the pins 50. Inthe form of Fig. l, even that is `minimized b'y the fact that the end ofthe sleeve' 58 engages the ring |04 and relieves thethrust upon the bearings 94 and 96. Engagement and disengagement of the various friction faces is non-critical since the paris are in slipping engagement but a very short time during the commencement of the shift. The friction faces have no relative slipping engagement in either pitch position. The shifting unit being axially symmetrical it, by its very nature, establishes its own balance during the assembly operation.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is, to be understood that other forms might be adapted, all coming withinl the scope of the claims which follow.

What is claimed is as follows:

l. In a high-low pitch propeller, an engine driven hub having a sleeved extension, blades socketed in the hub for pitch shifting movement and normally seeking a low pitch position, a pitch shifting unit carried by said hub eXtension and adapted to shift the blades to the high pitch position, said unit comprising a pistonand a cylinder both rotatable relative to the hub extension, and one thereof being axially movable with respect to the hub, a centrifugally responsive fluid contained in the chamber of the cylinder, and means remote from the propeller for arresting the rotation of the unit at the option of the pilot.

2. In a high-low pitch propeller, an engine driven hub having a sleeved extension, blades socketed in the hub for pitch shifting movement and normally seeking a low pitch position, a pitch shifting unit carried by said hub extension and adapted to shift the blades to the high pitch position, said unit comprising relatively movable piston and cylinder members chambered to contain a quantity of centrifugally responsive uid, both of said members being journalled for rotation relative to the hub and ono of the members being fixed against axial movement relative thereto, means transmitting axial movement of the other said member to pitch change of said blades, and remote control means for selectively controlling the rotation of said members whereby the application of centrifugal force upon the uid of the chamber is always under the control of the pilot.

3. In a high-low pitch propeller, an engine driven hub, blades socketed in the hub and having a journal bearing for pitch shifting movement. said blades normally seeking a low pitch position, an axially symmetrical `uid operated pitch shifting unit carried by the hub and acting in a fore and aft direction in response to centrifugal force while the hub fis rotating for shifting the bladesA to the high pitch position, and a manual controller for exposing the unit to and visolating it from' the application of centrifugal pitch shifting unit carried byfthe'hub and acting in a fore andaft direction in response to centrifugal force while the hub is rotating for shifting the blades to the high pitch position, and a manual controller for exposing the unit to and in a fore and aft direction in response to centrifuforce, said unit comprising cooperating annular piston and cylinder members arranged concen- A tric of the hub and defining a chamber of definite minimum capacity for housing a measured with the hub will displace the heavy fluidmedium from said minimum chamber to effect relative axial movement of the piston and cylinder, and pins responding to the relative movement of the piston members for shifting the blades to the high pitch position.

5, In a high-low pitch propeller, an engine driven hub, blades socketed in the hub and having ajournal bearing for pitch shifting movement, said blades normally seeking a low pitch position,. an axially symmetrical fluid operated pitch shifting unit carried by the hub and acting in a fore and aft direction in response to centrifugal force while the hub is rotating for shifting the blades to the high pitch position, and a manual controller for exposing the unit to and isolating it from the application of centrifugal force, said unit comprising a pair of telescoping members providing an annular chamber for reception oi' a quantity of fluid and each having an annular `face extending radially therefrom,

bearing means journalling the unit on the hub,

means permitting relative axial movement of one of the telescoping members, means translating axial movement of the said member to rotary movement of the blades 4in the hub, means including a pair of cooperating and normally engaging friction faces on the hub and unit for effecting rotation of the unit with the hub whereby fluid in the annular chamber is rotated to press outwardly and between the annular faces of the said members, and means for disengaging the friction faces whereby rotation of the unit is arrested and the fluid returned to the annular chamber.

6. In a high-low pitch propeller, an engine driven hub, blades socketed in the hub and having a journal bearing for pitch shifting movement, said blades normally seeking a low pitch position, an axially symmetrical fluid operated i pitch shifting unit carried by the hub and acting in a fore and aft direction in response to centrifugal force while the hub is rotating for shifting the blades to the high pitch position, and a manual controller for exposing the unit to and isolating it.from the application of centrifugal force, said unit comprises cooperating annular piston and cylinder members arranged concentric of the hub and dening a chamber of definite minimum capacity for housing a measured quantity of heavy fluid medium, saidpiston and cylinder having opposed parallel pressure faces radially outward of the chamber and adapted to be separated in response to centrifugal force applied to the contained heavy fluid mediumjmeans rotatably supporting the unit onthe hub and permitting axial movement of one of the members, and means for selectively'rotating the unit with l 0 the hub for high pitch shift of the blades', and for arresting the unit relative to the hub for low pitch-shift of the blades.

7. In a high-low pitch propeller, a power driven hub, blades socketed in the hub by journal and inward thrust bearings, for pitch shifting movement, said blades normally seeking a. low pitch position in response to centrifugal force and aerodynamic forces applied to the blade during hub rotation, a pitch shifting unit selectively operable to effect shift`of the blades to the high pitch position, said unit including an annular expansion chamber arranged concentric with the hub and adapted to be rotated by the hub, a fluid medium disposed in the chamber and operable upon the application of centrifugal force thereto to expand said chamber, and means controlling the rotation of the unit comprising a clutch face on the hub a friction face on the unit yieldingly urged to engage the clutch face, and a brake face selectively engageable with the friction face for disengaging it from the clutch face, and for arresting rotation of the unit.

8. In a high-low pitch propeller, a power driven hub, blades socketed in the hub by journal and inward thrust bearings, for pitch shifting movement, said blades normally tending to seek a low pitch position in response to centrifugal force and aerodynamic forces applied to the blade during hub rotation, a pitch shifting unit for opposing the tendencies of the blades and for shifting the blades to the high pitch position, said unit comprising relatively movable annular piston and cylinder` concentric of the hub, bearing means journalling the unit on the hub, and selective control means comprising a clutch face rotatable with the hub, a friction face rotatable with the unit and urged to engage the friction face whereby rotation of the hub rotates the unit, a brake face engageable with and disengageable from the friction face whereby the unit may be arrested against rotation with the hub, and a manually operated member for actuating the brake face, said unit having a chamber charged with a quantity of fluid of high density and operable upon rotation by the hub to exert pressure between the piston and cylinder for effecting blade shift to the high pitch position.

9. A blade shifting unit for aircraft propellers,

comprising in combination, a hub, a pair of telescopically related members rotatably mounted on the hub concentric with its axis said members being relatively axially movable and defining an annular chamber of radially stepped diameter, the larger diameter step'of lwhich is entirely collapsible upon relative axial movement of said members, in one direction, a centrifugally responsive liquid mass partially filling the smaller diameter step of the annular chamber, manually actuated means for selectively coupling the said related members and liquid mass for rotation with the hub, and for arresting their rotation, said liquid mass when rotated acting in response to centrifugal vforce for separating the members by enlargement of the larger diameter stepped portion in an axial direction of the annular chamber.

10. In a high-low pitch propeller, an engine driven hub, blades socketed in the hub and having a journal bearing for pitch shifting movement, said blades normally seeking a low pitch position, an axially symmetrical fluid operated pitch shifting unit carried by the hub and acting in a fore and aft direction in response to centrifugal force while the hub is rotating for shifting the blades to the high pitch position, and a manual controller for exposing the unit to and isolating it from the application of centrifugal force, said unit comprising cooperating piston and cylinder members deiining an expansible chamber of minimum capacity, a. uid medium in said chamber means providing a journal bearing for the unit on the hub and for relative movement of one of the members axially of the hub, means keying the piston and cylinder members against relative rotation and providing a friction face, a clutch face rotatable with the hub, means yieldingly urging the friction face into engagement with the clutch -face foreecting rotation of the unit with the hub whereby rotation of said unit effects rotation of the uid medium and axial movement of said cylinder, and a. brake face engageable with the friction face for arresting the rotation of .the unit. Y

JOSEPH STUART, III. WARREN D. BERKLEY.

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